Industrial Waste Water Treatment - balasubramanianbalasubramanian.yolasite.com/resources/Industrial Waste...Constituents of concern in waste water 26 BOD – Biological Oxygen Demand

Industrial Waste Water Treatment

Unit 5

Outline

• Water

• Water availability in the earth

• Distribution of available water in the earth

• Importance of industrial wastewater treatment

• Characteristics of waste water

• Constituents of concern in Industrial wastewater

• Various tests for wastewater

• Waste water treatment levels

• Advance waste water treatment methods

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Water

2

• Water is a transparent and nearly colourless liquid

• Most essential constituent for living organisms in the earth

• The molecular formula for water is H2O – One oxygen and two Hydrogen atoms

• It also occurs in nature as snow, glaciers, icepacks and icebergs, clouds, fog, dew, aquifers,

and atmospheric humidity.

“Life will not exist without water in our Mother Earth” – Anonymous

Water

3

Distribution of available water in the earth

Distribution of Water

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97.5% Salt Water

2.5% Fresh water

Salt water dominates

Most fresh water is unattainable

Source: FAO, 2009

About 97.5% of all water on earth is salt water

Only 2.5% of all the water on Earth is Fresh water


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70% Polar Ice caps

30% Underground

Source: FAO, 2009

2.5% Fresh water

Most fresh water is unattainable

Only 2.5% of all the water on Earth is Fresh water

Frozen icecaps

Around 70% of fresh water is frozen in Antarctica and green land icecaps

Underground

Most of the remaining fresh water lies too deep underground


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?% is available for

Human Consumption


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<1% is available for

Human Consumption

Water cycle

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Introduction

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Water cycle

Water Stress

https://phys.org/news/2014-08-scarcity-climate.html 10

https://phys.org/news/2014-08-scarcity-climate.html

Water stress occurs when the demand for water exceeds the available amount during a certain period or when poor quality restricts its use. Water stress causes deterioration of fresh water resources in terms of quantity

Water stress — European Environment Agency https://www.eea.europa.eu/themes/water/wise-help-centre/glossary-definitions/water-stress

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Water Stress

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- World wide

Really we need to

think?

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Water Stress – India

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Introduction

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Introduction

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Industrial water treatment - research database N

o. o

f Pap

ers

year

Source: Web of Science

Industries and Water

0

5

10

15

20

25

30

35

40

2001 2002 2003 2004 2005 2006 2007 2008 2009

No. of Papers published from 2001 to 2009

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Industries and Water Characteristics

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• Industrial wastewaters vary enormously in composition, strength and volume from

industry to industry and facility to facility within an industry

• Some wastewaters may be acidic or alkaline; contain oxygen depleting organic

materials, nutrients (e.g. phosphorous and nitrogen) that can cause

eutrophication.

• Suspended solids that can settle in receiving waters causing oxygen consuming

sludge deposits; be aesthetically unacceptable because of colour, taste, odour or

hazardous (toxic) components.

Industries and Water Characteristics

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• Therefore, it is essential to determine the characteristics (physical, chemical and

biological) of industrial wastewater.

Characteristics of industrial waste water

Water is characterized in terms of its

Physical, Chemical and Biological Composition Test used to asses the

constituents present in water

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Characteristics of waste water – Physical

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Characteristics of waste water – Physical

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Characteristics of waste water – Chemical (Inorganic)

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Characteristics of waste water – Chemical (Inorganic)

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Characteristics of waste water – Chemical (Organic)

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Characteristics of waste water – Biological

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Constituents of concern in waste water

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In general the two important characteristics of industrial wastewaters is the BOD and

COD apart from the characterises that are discussed previously.

BOD – Biological Oxygen Demand or Biochemical Oxygen Demand

(BOD)5 – 5day Biological Oxygen Demand

COD – Chemical Oxygen Demand


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• It is the amount of oxygen used by the microbes in the stabilization of a decomposable

organic waste material under aerobic (presence of air) conditions.

• The demand will be the oxygen required for the oxidation of organic (or carbonaceous

materials as given below:

𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂𝑂 𝑚𝑚𝑂𝑂𝑚𝑚𝑚𝑚𝑚𝑚𝑂𝑂 + 𝑂𝑂2𝐴𝐴𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 𝑚𝑚𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑚𝑚

𝐶𝐶𝑂𝑂2 + 𝐻𝐻2𝑂𝑂 + 𝑁𝑁𝐻𝐻𝑁 + 𝑁𝑁𝑚𝑚𝑁𝑁 𝑂𝑂𝑚𝑚𝑐𝑐𝑐𝑐𝑐𝑐 + 𝐸𝐸𝑂𝑂𝑚𝑚𝑂𝑂𝑂𝑂𝐸𝐸+ 𝑐𝑐𝑠𝑠𝑚𝑚𝑚𝑚 𝑠𝑠𝑚𝑚𝑜𝑚𝑚𝑂𝑂 𝑝𝑝𝑂𝑂𝑠𝑠𝑝𝑝𝑝𝑝𝑂𝑂𝑚𝑚𝑐𝑐


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• Since the amount of oxygen varies with the length of the time and the temperature,

the standard test for BOD is for 5 days at 20 °C and the BOD value yields is referred to

as the five day biochemical oxygen demand (BOD)5


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COD – Chemical Oxygen Demand

• BOD test requires 5 days duration; and in many cases, it is desired to have rapid test in

industrial wastewater treatment. Therefore, COD test is desired on such cases.

• The Chemical Oxygen demand (test) consists of oxidizing the sample (wastewater

containing organic matter) with strong oxidizing agent, potassium dichromate and

determining the amount of potassium dichromate used. Then the oxygen required in

the chemical oxidation can be determined.


Principal Constituents of concern in Industrial wastewater treatment

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Principal Constituents of concern in Industrial wastewater treatment

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Levels of wastewater Treatment

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Treatment Methods employed

• Physical – Screens, Coarse solids reducers, Grit separators, Flow equalizers,

Sedimentation, Clarifiers - Mixing, flocculation, Coagulation, Filters – Sand

Filtration, Membrane separations, and Adsorption

• Chemical – Ion exchange, Precipitation (oxidation and reduction)

• Biological Methods (Activated sludge, Aerobic and Anaerobic digestion)

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Advanced Treatment Methods employed

• Physical - Membrane separation

• Chemical – Ion exchange Precipitation /Advanced chemical oxidation

• Biological process – activated sludge, aerobic and anaerobic

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Treatment Methods employed – Physical

Screens (Screening)

• Screening is the device with openings, generally of uniform sizes that is used to

retain solids found in the wastewater.

• Its primary role is to remove coarse materials from waste water that could (a)

damage subsequent equipment in the treatment process and (b) reduce overall

treatment process reliability and effectiveness.

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Classification of Screens

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Screens

Coarse (6 to 150 mm)

Hand Cleaned Mechanically Cleaned

Chain Driven Reciprocating Rake Catenary Continuous

Belt

Micro (<0.5 μm)

Fine (<6μm)

Static wedge wire Drums



Grit separators (or Grit Chambers)

• Removal of grit from wastewater may be accomplished by the grit chambers.

• Grit chambers are designed to remove grit consisting of sand, gravel or heavy solid

materials.

• Grit chambers are mostly located after bar screens and before primary

sedimentation tank.

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Grit separators (or Grit Chambers)

• Grid chambers are provided to (i) reduce the formation of heavy deposits in

pipelines, channels and conduits; and (ii) reduces the frequency of digesters

cleaning caused by excessive accumulation of grit.

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Classification of Grit Chambers

Grit Chambers

Horizontal flow

Rectangular type

Square type

Aerated flow

Aerated grid type



Flow equalizers

• Flow equalization is a method used to overcome the operational problems caused

by flow rate variation to improve the performance of downstream processes and to

reduce size and cost of subsequent downstream treatment facilities.

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(a)

(b)


Sedimentation

• The objective of sedimentation is to remove readily settleable solids and reduce the

suspended solids.

• Sedimentation tanks are usually constructed of reinforced concrete and may be

circular, square or rectangular in plain view.

• Circular tanks may be ranging from 15 to 300 ft (4.57 t0 91.43 m) in diameter and

are usually from 6 to 16 ft (1.83 to 4.88 m) deep.

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Sedimentation

• The types of settling involved in sedimentation tank are (a) Type – I (Free settling), (b)

Type – II (Flocculate during settling), (C) Type – III (Zone or hindered settling),

(d) Type – IV (Compression settling)

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Sedimentation – (a) Type – I ( Free or discrete settling)

• It is the free settling of discrete, non flocculent particles in dilute suspensions.

• The particles settles as separate units and then no apparent flocculation or

interaction between the particles

• Hence the particles maintains individuality as it settles and does not interact with

other settling particles, and therefore does not change in size, shape or density.

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Sedimentation – (b) Type – II (Flocculate during settling)

• The settling of particles in dilute suspensions. The particles flocculate during

settling; thus they increase the size and settle at a faster rate.

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Sedimentation – (C) Type – III (Zone or hindered settling )

• The concentration of the particle in which they are so close together that inter

particle force hinder the settling of neighbouring particles.

• The particles remain in a fixed position relative to each other and all settle at

constant velocity.

• As a result the mass of the particle settles as a zone. At the top of the settling mass,

there will be distinct solid-liquid interface between settling particle and clarified

liquid.

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Sedimentation – (C) Type – IV (Compression settling)

• The settling of particles that are at such concentration that the particle touch each

other and settling can occur only by compression.

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Sedimentation – Type – I (a) Type – I ( Free settling)

• The types of settling involved in sedimentation tank are, (b) Type – II (Flocculate

during settling), (C) Type – III (Zone or hindered settling ), (d) Type – IV

(Compression settling)

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Clarifiers - Mixing, flocculation

• Flocculator clarifiers are often used in Industrial wastewater treatment, especially

where enhanced settling is required

• Inorganic chemicals or polymers can be added to improve flocculation

• These clarifiers are equipped with a paddle-type or low-speed mixer

• The gentle stirring causes flocculent particles to form and the solids are settled

down and scum are collected

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Coagulation

• Many industrial wastewater contain suspended or colloidal waste materials that are

too small to be effectively removed by gravity separation.

• Removal of colloidal particles becomes difficult by the fact that they usually have a

surface electrical charge that causes them to repel other particles, thus preventing

agglomeration to a size that could settle

• For these small suspended particles and colloids to be removed from suspension, the

surface charge must be destabilized and the particle must brought together so that

they can achieve a settlable size. This is the role of coagulation.

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• Coagulation result from the addition and rapid mixing of a coagulant with the

waste water to neutralize surface charges, collapse the surface layer around the

particle, and allow the particle to come together and agglomerate

• The resulting formation, called a floc, can more readily settle

• A number of coagulants are in common use. The most popular coagulants are

alum or aluminium sulfate and iron salts (ferric chloride, ferrous sulfate and ferric

sulfate)

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Flotation

• Flotation is essentially the reverse of sedimentation

• If the wastewater contains solids or immiscible liquids that are lighter than water,

they will float to the surface in a flotation tank, where they can be skimmed off

• Materials that are heavier than water, such as light solids or grease, may also be

removed by flotation if they are made more buoyant by the attachment of air

bubbles to their surfaces

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• In air flotation, air is bubbled into the bottom of the flotation tank or water

containing pressurized air is injected into the bottom of the tank so that air

bubbles are released from solution when the water pressure is reduced to that in

the tank

• The rising air microbubbles intercept suspended solids in the water; attach

themselves to the particles, making them more buoyant; and carry them to the

surface, where they are skimmed off.

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• Clarified liquid is removed from the bottom of the tank

• This process is particularly useful for material whose density is close to that of

water

• A common use of flotation is in the separation of free oil from waters

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Filters – Sand Filtration

• Filters are often used after settling tanks to remove solids that did not settle.

• There are many processes that fall under the heading of filtration.

• Among these are screens, granular media filters, vacuum filters, filter presses, and

various types of membrane filters

• Filtration processes can be used to remove suspended solids from industrial

wastewaters, as a stand-alone process to remove larger particles, as a pre-

treatment device before other treatment processes such as activated carbon

adsorption or membrane units, or following chemical treatment

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• Granular media filters consist of beds of granular media, such as sand, through which the wastewater passes.

• In industry, the filter medium is usually housed in a

cylindrical vessel; gravity filters can be used but usually the liquid flows down through the medium due to an applied pressure (see Figure)




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• The filter medium is supported by a bed of gravel to prevent short-circuiting and ensure uniform flow through the medium and out of the reactor.

• When build-up of accumulated solids causes pressure losses through the medium to become excessive, flow to the filter is stopped and the filter medium is backwashed by forcing water up through the medium.




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• The medium expands due to the buoyant forces from the rising water, contaminants become dislodged, and they flow out of the filter to waste.

• When the backwash water is turned off, the fluidized

filter medium settles back to the gravel base in a size-segregated fashion with the larger, heavier granules on the bottom and the lighter materials on top.




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• Granular media filters remove particles on the surface of the filter by straining and throughout the filter depth by a combination of straining, particle adsorption to the filter media's surfaces, and flocculation and settling within the pores between granules.

• As suspended solids are removed from the passing

water, the bed's porosity and permeability decrease, increasing removal efficiency but also increasing head losses.



Membrane separations • Membrane separation of solids from an industrial wastewater is actually a subset of filtration. • It can be used to separate colloidal and dissolved solids that are much smaller than those removed

by other filtration processes. • The membranes used have pores sufficiently small that even small molecules or ions can be

removed.

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Membrane separations

• The membranes can be made selectively permeable for specific materials so that

separations of these materials can be achieved.

• Membrane processes are very effective, but the rate of transfer across the

membrane is generally slow and pressure drops are high; large membrane areas are

generally required. • Membrane filtration includes a broad range of separation processes: ultrafiltration, dialysis, electro-dialysis, reverse osmosis, and so on.

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Effective range of various filtration and membrane processes



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Schematic representation of osmotic and reverse osmosis mechanisms



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Schematic representation of three types of reverse osmosis membrane systems (a) tubular membrane (b) hollow fibre membrane (c) spiral wound membrane



Adsorption

• Adsorption consists of transferring the contaminant from the aqueous waste phase to the surfaces of an adsorbent material. • The most commonly used adsorbent is activated carbon because of its large surface

area, ability to sorb a wide variety of compounds, and its low cost relative to other comparable adsorbents.

• In essence, adsorption occurs primarily due to van der Waals' forces, molecular forces of attraction between the solute and the solvent (physical adsorption).

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Adsorption

• When the forces of attraction between the solute and the sorbent are greater

than those between the solute and water, the solute will come out of solution and attach itself to the sorbent surface.

• Some adsorption also occurs because of chemical reactions between the solute and active groups on the activated carbon pore surface (chemical adsorption), but this is usually minor in comparison to physical adsorption. Chemical adsorption is usually irreversible.

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Ion Exchange

• Ion exchange is a chemical treatment process used to remove unwanted ionic

species from wastewater.

• In industrial wastewater treatment, it is predominantly used to remove cations (i.e., heavy metals) from solution, but it can also be used to remove anions such as cyanide, arsenates, and chromate.

• As the name implies, ion exchange works by exchanging undesirable cations or anions in solution with less harmful ones from an ion exchange resin.

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Treatment Methods employed – Chemical


Ion Exchange

• Thus the harmful ions are removed from the aqueous stream and attached to the

resin. • The ions are not destroyed but rather are removed from the waste stream and

concentrated on the resin, where they can be more easily handled.

• The exchange reaction is reversible, and the exchanged contaminants can later be removed from the resin, making the resin available for reuse.

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Ion Exchange • Ion exchange resins consist of inorganic minerals with a deficit of positive atoms

within the crystalline structure, known as zeolites, or synthetic organic polymeric materials that have ionizable functional groups, such as sulfonic, phenolic, carboxylic, amine, or quaternary ammonium.

• Zeolites are essentially all cation exchange materials (they exchange positively charged ions); the negatively charged zeolite surface is counterbalanced by exchangeable cations in solution next to the negative sites.

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Ion Exchange • These loosely held cations can be

readily replaced by higher valence state cations (i.e., heavy metals) in the wastewater.

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Schematic representation of Demineralization of water by ion exchange



Precipitation (Chemical oxidation and reduction)

• Chemical oxidation or reduction (redox) systems are used to treat several

industrial wastewater types. • Recent research on advanced oxidation processes (AOPs) has been promising and

may soon allow oxidation processes to be used on a wider scale.

• Chemical oxidation is a process in which one or more electrons are transferred from the chemical being oxidized to the chemical initiating the transfer (the oxidizing agent).

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Precipitation (Chemical oxidation and reduction)

• Thus oxidation of a substance results in the loss of electrons from the substance,

whereas reduction of a substance results in a gain of electrons in the substance.

• Oxidation and reduction reactions must be coupled together because free electrons cannot exist in solution.

• In the case of industrial waste treatment, pollutants are oxidized or reduced to products that are less toxic, more readily biodegradable, or more readily removed by adsorption.

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Treatment Methods employed Precipitation (Chemical oxidation and reduction)

• There are a number of chemical oxidizing and reducing agents and several

commonly accepted treatment systems that they can be applied to. Among the more common oxidizing agents are ozone, hydrogen peroxide, chlorine, and potassium permanganate.

• These are currently used to oxidize cyanides, sulfides, phenols, pesticides, and some other organic compounds. Typical reducing agents are ferrous sulfate, sodium metabisulfite, sodium borohydride, and sulfur dioxide.

• They are predominantly used to reduce a metal, particularly chromium, to its less soluble and less toxic trivalent state.

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Precipitation (Chemical oxidation and reduction) for the removal of chfomium

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Schematic of the chromium reduction and precipitation




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Schematic of the ozone oxidation and UV radiation




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Schematic of the advanced oxidation process involving the use of ozone and hydrogen peroxide (H2O2)


References

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1. https://en.wikipedia.org/wiki/Water

2. Rick Smolan and Jennifer Erwitt, Blue Planet Run: The race to provide safe drinking water to the world, www.bluplanetrun.org

3. Corcoran, E. (Editor); Nellemann, C. (Editor); Baker, E. (Editor); Bos, R. (Editor); Osborn, D. (Editor); Savelli, H. (Editor) (2010): Sick Water? The central role of wastewater management in sustainable development. A Rapid Response Assessment. United Nations Environment Programme (UNEP), UN-HABITAT, GRID-Arendal

4. Water Resources Institute 5. Metcalf and Eddy, Wastewater Engineering: Treatment and Reuse, 4th Ed., McGraw, Hill 6. Bishop, Pollution Prevention Fundamentals and Practice , McGraw Hill

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Industrial Waste Water Treatment - balasubramanianbalasubramanian.yolasite.com/resources/Industrial Waste...Constituents of concern in waste water 26 BOD – Biological Oxygen Demand